The Greek philosopher Anaxagoras (ca. 500-ca. 428 BC) was the first to formulate a molecular theory of matter and to regard the physical universe as subject to the rule of rationality or reason.

Anaxagoras was born on the Ionian coast of Asia Minor in the town of Clazomenae, near Smyrna (now Izmir, Turkey). Nothing is known about his life before the age of 20, when he began to study philosophy. About 462 he moved to Athens, which was rapidly becoming an attractive cultural center. Anaxagoras was the first philosopher to take up residence in Athens. His teachings influenced the playwright Euripides, but his most famous pupil was Pericles, who dominated the political life of Athens during the 30 years Anaxagoras lived there.

Anaxagoras did not believe that the sun and moon were divinities, as the Greeks did, and he was prosecuted for his teachings. He returned to Asia Minor to a town allied with Athens, Lampsacus (now Lapseki, Turkey). Here he was treated with respect, and his memory was still honored a century after his death.

"About Nature"

Anaxagoras's views are preserved only in excerpts and summaries, more or less authentic. His book, written in prose, was entitled About Nature. It started with this assertion: "All things were together, infinite in number." This abrupt beginning was intended as a blunt contradiction of an earlier contention that the universe was "one continuous whole, which was not in the past," there being only an everlasting unchanging present. In direct opposition to this perpetually static monism, Anaxagoras propounded a constantly changing pluralism. He was the first philosopher to declare the number of separate things to be infinite (the universe as a whole having already been described as infinite).

Each of Anaxagoras's infinitely numerous separate things could be divided and further subdivided endlessly. All the things that were together were infinite not only in number but also in smallness: "Of what is small, there is no smallest part, but always a smaller." By contrast with the thinkers who maintained that matter consisted of those smallest units which were the atoms or indivisible particles, Anaxagoras believed in the infinite divisibility of matter. Nevertheless, as often as this process of subdivision was repeated, the resulting product always emerged as a unit of matter, however infinitesimally small it might be. In this sense Anaxagoras may be regarded as the author of the first molecular theory of matter.

Concept of Mind

His infinitely divisible things, infinite in number, were originally all together. How they had come together and where they had come from were questions not propounded by Anaxagoras. Thus, his universe began with a vast indiscriminate jumble or species of magma, which in the course of time was set whirling by Mind: "The whole rotation was controlled by Mind in such a way that in the beginning there was a vortical motion. At first the turning began on a small scale, but it spins more widely and it will spin even more widely."

What is more, Anaxagoras's Mind itself was not an insubstantial, incorporeal, exclusively mental, spiritual, or divine entity. Unlike a theist, Anaxagoras described his cosmic Mind as being the "most delicate and purest of all things." Nor was Anaxagoras a dualist in the conventional sense of one who counterposes mind against matter, for he declared that "Mind even now is where all other things are too, in the surrounding plenitude as well as in the things that have been assembled and those that have been disassembled."

Anaxagoras rebuked "the Greeks for not thinking correctly about birth and death, since nothing is born or dies; on the contrary, everything is assembled out of existing things and then dissolved. Accordingly, the Greeks would properly call birth 'combination' and death 'dissociation.'" In other words, any individual thing comes into being by combining preexisting components and is dissolved into its constituent parts when its existence is terminated. While individuals come and go, the building blocks or molecular particles persist. They move about freely and enter into new combinations without undergoing any change in their essential nature.

This unceasing flux of migration, combination, dissolution, and recombination is not senseless or chaotic. For Anaxagoras, cosmic Mind "is infinite and absolute; it possesses perfect knowledge of everything, exerts the greatest power, and dominates all living things, the biggest and the smallest." Since all life in Anaxagoras's universe is under the control of Mind, each molecular interchange occurs according to rule. His universe therefore is thoroughly rational, and what he called "Mind" is analogous to what was afterward termed the "laws of nature."

Split-Level Universe

To this overall vision of an orderly cosmos, Anaxagoras contributed some valuable details. Of these, unquestionably the most spectacular was his discovery that the moon does not shine by its own light. By contrast, in the Hebrew Bible the moon was the lesser of the two great lights; like the sun, which was the biblical greater light, the Hebrew moon was self-luminous. Presumably it is because the earth too receives light from the sun that Anaxagoras declared the moon to be earth. His earth and moon resembled each other also in having "flat areas and depressions." Anaxagoras's amazingly prescient description of the moon's ups and downs and his implicit denial that the lunar surface was perfectly spherical waited more than 2,000 years for visual confirmation by Galileo's telescope, and then more than 3 additional centuries for the direct physical proof provided by the American astronauts on the moon.

Anaxagoras believed (mistakenly) that the sun was a red-hot stone. Apparently generalizing from the instances of the sun and moon, he asserted that all the heavenly bodies were stone. His opinion that rock was the material of those bodies may have been inspired by the fall of a huge meteorite, said to have been as big as a wagon, near the Dardanelles when he was a young man. Since Anaxagoras correctly classified the meteorite as an object fallen from the sky to the earth, his universe was all alike. Later the cosmos was divided into an ethereal heaven, reserved for divinities, and the coarse earth, to which mere mortals were consigned. The painful process of reunifying this post-Anaxagorean split-level universe amounted to a return to the one world of Anaxagoras.

Further Reading

• Daniel E. Gershenson and Daniel A. Greenberg, Anaxagoras and the Birth of Physics (1964), is a collection of the ancient references to Anaxagoras, arranged in chronological order and analyzed as to content; the bibliography is annotated. Also useful is Felix M. Cleve, The Philosophy of Anaxagoras (1949). Among the general books on early Greek philosophy that discuss Anaxagoras are John Burnet, Early Greek Philosophy (1892; 4th ed. 1930); Theodor Gomperz, Greek Thinkers: A History of Ancient Philosophy (3 vols., 1896-1909; trans., 4 vols., 1901-1912); and G. S. Kirk and J. E. Raven, The Presocratic Philosophers: A Critical History with a Selection of Texts (1962).
• Schofield, Malcolm., An essay on Anaxagoras, Cambridge Eng.; New York: Cambridge University Press, 1980.
• Anaxagoras., The fragments of Anaxagoras, Meisenheim am Glan: Hain, 1981.